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Multiple sclerosis (MS), the leading cause of disability in young adults, is an inflammatory disease of the central nervous system characterized by localized areas of demyelination. Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase that has been shown to be implicated in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. Interestingly, ASK1 signaling regulates glial cell interactions and drives neuroinflammation in EAE mice. To further investigate its clinical significance, in the present study, we examined the activation of ASK1 in the post-mortem brain of MS patients. ASK1 activation was found in active lesions of the corpus callosum in both microglia/macrophages and astrocytes. Moreover, ASK1 activation in astrocytes was higher than that in microglia/macrophages, which was in line with our findings in EAE mice. Our results suggest an important role of ASK1 in glial cells, indicating that ASK1 might be a good therapeutic target for MS., (© 2024 Japanese Society of Neuropathology.)

Cerebral ischemia may lead to axonal injury not only at the site of the primary lesion but also in a region remote to the site of insult. In this study, we investigated the effect of herniation on the development of axonal injury at a site remote to the primary lesion during the acute phase of cerebral ischemia. We obtained postmortem brains of 13 cases with acute phase of unilateral cerebral infarction in the territory of the internal carotid artery or middle cerebral artery and seven controls. We classified the brain tissues into herniation and non-herniation groups. Then we examined whether axonal and ischemic changes existed in the corpus callosum contralateral to the ischemic hemisphere and the upper pons. In the herniation group, we detected white-matter lesions by Klüver-Barrera staining, microglial loss by immunohistochemistry for ionized calcium-binding adaptor molecule 1, and axonal injury by immunohistochemistry for amyloid precursor protein. However, none of the aforementioned findings were observed in the non-herniation group. These findings suggest the existence of regional overlap in axonal and ischemic pathologies in remote regions in the presence of herniation. We concluded that herniation may play a significant role in the development of axonal and ischemic changes in the remote region. Our results suggest that axonal injury in a remote region may result from expanded ischemic lesions due to herniation., (© 2023 Japanese Society of Neuropathology.)

Amyloid-β precursor protein (APP) immunohistochemistry has been used to detect axonal injury in forensic neuropathology. However, axonal injury caused by cerebral ischemia has not been investigated by APP immunohistochemistry in detail. In particular, it is unknown if there is a correlation between the prognosis of cerebral ischemia and the distribution of axonal injury detected by APP immunohistochemistry. To address this issue, we compared the distribution of APP-immunoreactive axons in autopsy brains including lesions of acute phase of cerebral infarction in the territory of the middle cerebral artery (MCA) or internal carotid artery (ICA) with the degree of severity. The presence or absence of a midline shift was used as an indicator of the severity of cerebral ischemia. We identified a difference in the distribution of APP-immunoreactive axons between cases with and without a midline shift. In both the groups, APP-immunoreactive axons were detected at the margin of the ischemic lesions; however, only in cases with a midline shift, intense APP-immunoreactive axons were also found in areas other than the MCA and ICA territories, including the white matter of the cerebral hemispheres ipsilateral and contralateral to the ischemic lesions. This distribution was different from that of acute global cerebral ischemia cases reported previously. Our results indicate that the distribution of APP-immunoreactive axons differs according to the severity and type of cerebral ischemia, suggesting that the distribution of APP-immunoreactive axons is associated with the prognosis of cerebral ischemia., (© 2022 Japanese Society of Neuropathology.)

Nasu-Hakola disease (NHD) is a rare autosomal recessive disorder, characterized by formation of multifocal bone cysts and development of leukoencephalopathy, caused by genetic mutations of either DNAX-activation protein 12 (DAP12) or triggering receptor expressed on myeloid cells 2 (TREM2). Although increasing evidence suggests a defect in microglial TREM2/DAP12 function in NHD, the molecular mechanism underlying leukoencephalopathy with relevance to microglial dysfunction remains unknown. TREM2, by transmitting signals via the immunoreceptor tyrosine-based activation motif (ITAM) of DAP12, stimulates phagocytic activity of microglia, and ITAM signaling is counterbalanced by sialic acid-binding immunoglobulin (Ig)-like lectins (Siglecs)-mediated immunoreceptor tyrosine-based inhibitory motif (ITIM) signaling. To investigate a role of CD33, a member of the Siglecs family acting as a negative regulator of microglia activation, in the pathology of NHD, we studied CD33 expression patterns in five NHD brains and 11 controls by immunohistochemistry. In NHD brains, CD33 was identified exclusively on ramified and amoeboid microglia accumulated in demyelinated white matter lesions but not expressed in astrocytes, oligodendrocytes, or neurons. However, the number of CD33-immunoreactive microglia showed great variability from case to case and from lesion to lesion without significant differences between NHD and control brains. These results do not support the view that CD33-expressing microglia play a central role in the development of leukoencephalopathy in NHD brains., (© 2015 Japanese Society of Neuropathology.)

Dysembryoplastic neuroepithelial tumor (DNT) is a benign glioneuronal tumor, occurring in children and adolescents, typically associated with drug-resistant partial seizures. Pathologically, DNT is characterized by a specific glioneuronal element that is comprised of oligodendroglia-like cells (OLC) and floating neurons. The definition of DNT is currently controversial and the incidence of DNT varies among institutions. In this study we characterize the morphologic profiles of OLC and floating neurons by performing immunohistochemical and morphometric studies on seven cases of a simple form of DNT. While a majority of OLC was positive for oligodendrocyte transcription factor 2 (Olig2), only floating neurons and a few small cells were positive for neuronal nuclear antigens (NeuN). Double immunofluorescence studies revealed co-localization of Olig2 and galectin 3 in OLC, but no co-localization of Olig2 and NeuN. The distribution pattern of NeuN-positive nuclei within the tumor tissue was not different from that in the adjacent neural tissue. A section cut perpendicular to the cortex stained with NeuN showed a continuous laminar arrangement with the adjacent cortex. Densities of NeuN-positive nuclei from tumors embedded in the white matter were significantly lower than those from tumors in the gray matter. Our results suggest that the NeuN-positive small and large cells observed within the specific glioneuronal element are in fact entrapped granular and pyramidal cells within the cortex and that OLCs are essentially glial and not neuronal in nature. DNT is thus a pure glial tumor rather than a glioneuronal tumor, that is, the equivalent of non-infiltrating oligodendroglioma, grade I., (© 2013 Japanese Society of Neuropathology.)

Nasu-Hakola disease (NHD) is a rare autosomal recessive disorder, characterized by progressive presenile dementia and formation of multifocal bone cysts, caused by a loss-of-function mutation of DNAX-activation protein 12 (DAP12) or triggering receptor expressed on myeloid cells 2 (TREM2). TREM2 and DAP12 constitute a receptor/adaptor complex on myeloid cells. The post-receptor signals are transmitted via rapid phosphorylation of the immunoreceptor tyrosine-based activating motif (ITAM) of DAP12, mediated by Src protein tyrosine kinases, followed by binding of phosphorylated ITAM to Src homology 2 (SH2) domains of spleen tyrosine kinase (Syk), resulting in autophosphorylation of the activation loop of Syk. To elucidate the molecular mechanism underlying the pathogenesis of NHD, we investigated Syk expression and activation in the frontal cortex and the hippocampus of three NHD and eight control brains by immunohistochemistry. In NHD brains, the majority of neurons expressed intense immunoreactivities for Syk and Y525/Y526-phosphorylated Syk (pSyk) chiefly located in the cytoplasm, while more limited populations of neurons expressed Src. The levels of pSyk expression were elevated significantly in NHD brains compared with control brains. In both NHD and control brains, substantial populations of microglia and macrophages expressed pSyk, while the great majority of reactive astrocytes and myelinating oligodendrocytes did not express pSyk, Syk or Src. These observations indicate that neuronal expression of pSyk was greatly enhanced in the cerebral cortex and the hippocampus of NHD brains, possibly via non-TREM2/DAP12 signaling pathways involved in Syk activation., (© 2011 Japanese Society of Neuropathology.)

Nasu-Hakola disease (NHD) is a rare autosomal recessive disorder, characterized by progressive presenile dementia and formation of multifocal bone cysts, caused by genetic mutations of DNAX-activation protein 12 (DAP12) or triggering receptor expressed on myeloid cells 2 (TREM2). TREM2 and DAP12 constitute a receptor/adapter signaling complex expressed on osteoclasts, dendritic cells (DC), macrophages and microglia. Previous studies using knockout mice and mouse brain cell cultures suggest that a loss-of-function of DAP12/TREM2 in microglia plays a central role in the neuropathological manifestation of NHD. However, there exist no immunohistochemical studies that focus attention on microglia in NHD brains. To elucidate a role of microglia in the pathogenesis of NHD, we searched NHD-specific biomarkers and characterized their expression on microglia in NHD brains. Here, we identified allograft inflammatory factor 1 (AIF1, Iba1) and sialic acid binding Ig-like lectin 1 (SIGLEC1) as putative NHD-specific biomarkers by bioinformatics analysis of microarray data of NHD DC. We studied three NHD and eight control brains by immunohistochemistry with a panel of 16 antibodies, including those against Iba1 and SIGLEC1. We verified the absence of DAP12 expression in NHD brains and the expression of DAP12 immunoreactivity on ramified microglia in control brains. Unexpectedly, TREM2 was not expressed on microglia but expressed on a small subset of intravascular monocytes/macrophages in control and NHD brains. In the cortex of NHD brains, we identified accumulation of numerous Iba1-positive microglia to an extent similar to control brains, while SIGLEC1 was undetectable on microglia in all the brains examined. These observations indicate that human microglia in brain tissues do not express TREM2 and DAP12-deficient microglia are preserved in NHD brains, suggesting that the loss of DAP2/TREM2 function in microglia might not be primarily responsible for the neuropathological phenotype of NHD., (© 2010 Japanese Society of Neuropathology.)

Glial cytoplasmic inclusions (GCIs) and microglia were quantified in 12 cases of multiple system atrophy (MSA) with special reference to their association with histologically defined lesion severity. The targets of the analysis were white matter (cerebellum, pontine base) and gray matter (putamen, substantia nigra). First, the lesion severity was defined: for white matter, the degree of demyelination and tissue rarefaction were semi-quantified on Klüver-Barrera (KB) sections as grade I (mildly injured), II (moderately injured), and III (severely injured); for gray matter, neurons and astrocytes were counted on KB and glial fibrillary acidic protein-immunostained sections, respectively. Next, the GCI burden was quantified on sections immunostained for alpha-synuclein, phosphorylated alpha-synuclein, and ubiquitin and the microglial burden was quantified on sections immunostained for HLA-DR. In white matter, the GCI and microglial burdens were the greatest when the tissue injury was mild and/or moderate (grade I and/or grade II), and they became less prominent when the tissue injury became more severe (grade III). In gray matter, in contrast, the GCI and microglial burdens failed to show significant correlations with the lesion severity. Our result suggests that the amount of GCIs as well as that of microglia is reduced when the tissue injury becomes severe in vulnerable white matter areas, but not in vulnerable gray matter areas, of MSA. It also suggests that there seems to be a difference between gray matter and white matter in the way GCIs and microglia participate in the degenerative process of MSA.

As neurosurgical treatments have been increasingly applied to patients who have intractable epilepsy, much knowledge on pathological changes in surgically removed brain tissues have become clearer in recent years, as well as on the neuroimaging findings which are analyzed with a variety of techniques, including computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission computed tomography (SPECT) in combination with digital imaging and communication in medicine (DICOM), statistical parametric mapping (SPM), subtraction ictal SPECT coregistered to MRI (SISCOM) and/or PET-guided intraoperative navigation system, as mentioned in detain in another article in this issue by Maehara et al. Representative and relatively common diseases, treated by epilepsy-surgery, are as follows; hippocampal sclerosis, amygdaloid sclerosis, coarse and macroscopic brain malformation (focal cortical dysplasia, hemimegalencephaly, tuberous sclerosis), tumors (dysembryoplastic neuroepithelial tumor, ganglioglioma, etc.), destructive lesions and the others. It is a fact, however, that there remains many problems in the diagnostic criteria or histological grading systems, especially in various cortical dysplasias described above. On the other hand, histologically minor but clinically serious lesions have become to be known through careful observations on surgically removed tissues which showed no neuroradiological findings. A good well-known example is microdysgenesis of the cerebrum which is characterized by the presence of both the white mater ectopic neurons and the vascular meandering abnormalities with glial satellitosis. There must be another important histological phenotypes of microdysgenesis, except the above-mentioned ones, that are not yet established at present. Therefore, it is believed that there remains various problems on the diagnostic neuropathology of epileptic lesions with or without neuroimaging findings in which we have to give answers in a few days to come.

A 19-year-old female patient, who had exhibited esotropia, mild cerebellar ataxia, mild mental retardation, and cerebellar atrophy on magnetic resonance images at the age of 15, developed signs of acute encephalopathy, and thereafter died of disseminated intravascular coagulation on the day of her admission. Both her mother and sister suffered from attacks of hemiplegic migraine, mild mental retardation, and cerebellar ataxia. Neuropathological examinations revealed acute changes in the widespread cerebral cortex, chronic degenerative changes in the anterior lobe of the cerebellar vermis, axonal spheroids in the Goll's nucleus, pseudo-calcinosis in the globus pallidus, and glial bundles in the cranial nerves. The most fascinating features were changes of Purkinje cells, such as cactuses (asteroid bodies, dendritic expansions), somatic sprouts, and torpedoes. These changes may be characteristic of familial hemiplegic migraine with cerebellar atrophy, as well as the other metabolic diseases, such as Menkes' kinky hair disease, infantile (Tay-Sachs type) amaurotic idiocy, organic mercury intoxication, and mitochondrial encephalopathy, of which cases often exhibit such pathological changes of Purkinje cells. Therefore, familial hemiplegic migraine may share some metabolic abnormalities with the diseases mentioned above.

DRPLA is a rare neurodegenerative disorder caused by CAG triplet elongation on chromosome 12p. In addition to neurodegeneration of both the dentatorubral and pallidoluysian systems, there is cerebral white matter damage, especially in older cases. Intracellular accumulation of DRPLA protein is widespread in the central nervous system, and DRPLA protein has been shown to immobilize glyceraldehyde 3-phosphate dehydrogenase (GAPDH), which regulates glycolysis and controls mRNA of tissue-type plasminogen activator (tPA) in tissue restoration. However, little is known about the pathogenesis regarding the formation of cerebral white matter damage in DRPLA. Therefore, the pathology of this damage was investigated by examining markers of glycolysis and related processes. Nine clinically and pathologically confirmed DRPLA cases were used in the present study. CAG triplet elongation on chromosome 12p was confirmed in all cases where tissue was available for genotyping (seven cases). PAS and immunohistochemistry with antibodies to GFAP, GAPDH and endothelin-1 were used to demonstrate astrocytosis. The polysaccharides storage state with PAS-positive astrocytes was detected in seven cases. GAPDH- and endothelin-1-positive endothelium and astrocytes were observed in two cases with GFAP-positivity. Based on the biochemical process together with the present results, GAPDH and endothelin-1 immunoreactivity is associated with this damage and the mismetabolism of polysaccharides caused by CAG triplet elongation on chromosome 12p may contribute to the formation of the cerebral white matter damage in DRPLA.